Septic Arthritis

» Orthopaedic

Overview

Septic arthritis refers to infection in a joint; it is usually caused by bacteria but can be caused by fungi or mycobacteria. Septic arthritis due to bacterial infection is often a destructive form of acute arthritis.

Definition
Arthritis: Inflammation of joint
Arthrosis: Degeneration of joint
Septic Arthritis: Infection of joint

Risk Factors

Age >80 years
Diabetes mellitus
Rheumatoid arthritis
Presence of prosthetic joint
Recent joint surgery
Skin infection
Intravenous drug abuse, alcoholism
Prior intraarticular corticosteroid injection

Signs and Symptoms

Monoarthritic Joint (Oligoarticular or polyarticular infection occurs in approximately 20% of septic joint infections)

Severe pain
Swelling
Warmth
Restricted movement
Fever
Chills

Remember The knee is involved in more than 50 percent of cases.

Remember Septic arthritis can result in irreversible joint damage within 48 hours of the onset of infection due to the proteolytic enzymes of the white blood cells that flood the infected synovial space.

Differential Diagnosis

Monoarthropathy	Oligoarthropathy	Polyarthropathy
Septic arthritis	Crystal arthritis	Rheumatoid arthritis
Crystal arthritis (Gout)	Psoriatic arthritis	Viral Arthritis
Osteoarthritis (can be mono-poly)	Reactive arthritis	Autoimmune connective tissue disease (ie. SLE)
Trauma (Haemarthrosis)	Ankylosing spondylititis	Vasculitides (ie. Polymyalgia Rheumatica)

Other

Transient synovitis
Osteomyelitis may also mimic septic arthritis in its presentation
Trauma
Tumours

Transient synovitis: or Irritable hip, is a common disorder of childhood which presents with the acute onset of hip pain and a limp that gradually resolves. The history is one of an acute onset of hip pain and a limp, followed by knee pain and inability to weight bear. On examination, the affected leg tends to be held in the position of greatest ease, typically, one of flexion, abduction and slight external rotation.

Osteomyelitis: The patient usually presents with pain, malaise and a fever and in neglected cases toxaemia may be marked. Sometimes a history of preceding skin lesion, an injury or sore throat may be obtained, the limb is held still and there is acute tenderness near the largest joint. Even gentle manipulation is painful and joint movement is restricted. Local redness, swelling, warmth and oedema are later signs and signify the presence of pus.

Investigations

Patients with suspected septic arthritis should be referred urgently and immediately for hospital specialist review.

Joint aspiration - Synovial Aspiration
FBC
EUC
CRP/ESR
Blood cultures
Urinalyis
Anti-streptolysin O titre

Synovial fluid analysis
	Aetiology	Colour and Clarity	WBC (mm³)
Normal	Normal	Clear and transparent	<200
Inflammatory	Gout	Yellow and traslucent-opaque	2000-100,000
Septic	Bacteria	Yellow/green and opaque	>25,000 - >100,000
Haemorrhage	Trauma	Red and Bloody	200-2000

Diagnosis - Identification of bacteria in the synovial fluid.

Aetiology

Common

Staphylococcus aureus - In patients with comorbid joint disease or recent joint surgery
Group A Streptococcus
Neisseria gonorrhoeae - Sexually active adult

Other

Anaerobic microbes
Fungal

Remember In children Staphylococcus aureus is the most common pathogen. Other causative organisms include group A Streptococcus and Enterobacter species. Haemophilus influenzae septic arthritis may occur in children who have not been vaccinated.

Pathophysiology

Septic arthritis involves bacterial infection of a synovial joint.

Haematogenous bacterial spread is the most common cause of septic arthritis
Osteomyelitis of adjacent bones may also result in joint infection
Direct inoculation via penetrating injuries or surgery can occur

Proteolytic enzymes released by host inflammatory cells and certain bacteria cause cartilage destruction.

Management

Broad Spectrum Antibiotic therapy
NSAIDs
Joint drainage and lavage of the joint
Tailored antibiotic regime following identification of microbe

Complication and Prognosis

Complications

Antibiotic allergic reaction
Osteomyelitis
Dislocation – a tense effusion may cause dislocation of a joint.
Joint destruction
Joint destruction in children:
- Epiphyseal destruction. In neglected infants, the largely cartilaginous epiphysis may be destroyed, leaving unstable psudeoarthrosis.
- Growth disturbance - Physeal damage may result in shortening or deformity.
- Ankylosis - If articular cartilage is eroded, healing may lead to ankylosis.

Prognosis Delayed or inadequate treatment can lead to irreversible joint destruction and subsequent disability (<48hours). There is also an estimated case fatality rate of 11%.